1. Field of the Invention
The present invention relates to a lithographic printing method and a printing press which use on-machine development type plates. More specifically, the present invention relates to a lithographic printing method which has very little paper spoilage at the start of printing and a short prep time, and thus has a very high productivity. The invention relates also to a printing press that is well-suited for use in such a method.
2. Description of the Related Art
By employing printing plates capable of being developed on the printing press with dampening water and/or ink, typically referred to as “on-machine development type plates,” as a way to improve the productivity of lithographic printing, it has been possible to dispense with a development step in which a developer is used, thereby shortening the platemaking time. Moreover, eliminating the need for a processing machine and developer has a number of advantages, such as lowering costs.
However, the use of a method in which an on-machine development type plate is employed and in which development is carried out with dampening water and/or ink (see, for example, JP 2000-52634 A: the term “JP XX-XXXXXX A” as used herein means an “unexamined published Japanese patent application”) has the following drawbacks.
For example, with on-machine development type plates of the sort from which non-image areas of the image recording layer are removed, after the image has been recorded, the image recording layer in non-image areas is removed with dampening water and/or ink, leaving the hydrophilic surface of the plate exposed. Yet, instead of being completely removed, residues of the image recording layer sometimes continue to adhere to the plate surface in non-image areas.
Because these portions of the image recording layer that continue to adhere instead of being removed are oleophilic, ink deposits thereon, contaminating the non-image areas. As printing proceeds, such residues are removed by the dampening water and thus cease to contaminate. The paper which is used until scum ceases following the start of printing is generally referred to as “spoilage.” During this period, scum-free impressions cannot be obtained.